1. Field of the Invention
This invention relates to an antenna system for use in an automotive vehicle employing a planar antenna.
2. Description of the Related Art
Generally, it is desired that an antenna for use in an automotive vehicle is mounted on the vehicle body so that it does not project outside the body of the automotive vehicle in view of the factors such as the aerodynamic characteristic, the appearance of the vehicle, and the convenience of washing the vehicle body, etc. Thus, it has been proposed in the past to mount a planar antenna on the vehicle body, since the use of a planar antenna is advantageous especially in respect of the aerodynamic characteristic.
Recently, it has been desired to set up a mobile station for receiving radio waves transmitted from a satellite by using an antenna system mounted on an automotive vehicle or a ship, etc. It is necessary for the antenna system mounted on the mobile station to continuously track the satellite at all times. As an antenna system for use in a ship, the Cassegrain antenna system is proposed in which two axes, which make azimuth and elevation angles, respectively, are driven and which operates to detect deviations of the antenna beam by the conical scanning system thereby to drive the two axes, whereby automatic tracking is effected to have the antenna beam always pointed at the satellite (Published in the Journal of Japanese Electronic Communication Society, October, 1984).
When mounting a planar antenna on the vehicle body, it is necessary to cover the planar antenna with a radome in order to protect the antenna from wind and/or rain in bad weather, or from water at the time of car washing. In this case, it becomes necessary for the radome to satisfy the requirements of the aerodynamic characteristic, the appearance of the vehicle body, etc. Further, when the planar antenna mounted on the vehicle body is rotated within a plane, in which the planar antenna is placed when it has been installed, in order to effect the adjustment of an azimuth angle of the antenna beam, there occurs a problem of selecting a suitable place of installation of a driving device required to rotate the antenna.
In addition, when receiving radio waves from a satellite by an antenna system mounted on an automotive vehicle, the use of a conventional antenna system for a ship as an antenna system for an automotive vehicle is substantially impossible in view of the aerodynamic characteristic, external appearance, etc. of the vehicle, since a conventional antenna system for a ship generally has great size and heavy weight.